Background/Objectives: Physical inactivity and sedentary lifestyles remain leading behavioral risk factors for chronic disease across generations. Mothers with young children face unique barriers to exercise, including time constraints, fatigue, and limited access to supportive environments. Lion Hearts was developed to address these barriers through a family-centered, community-based approach that integrates physical activity, strength training, and health education. This protocol describes the systematic application of the Intervention Mapping (IM) framework to develop Lion Hearts, a multigenerational CrossFit-based program for mothers and children. Methods: Following the first four steps of the IM framework—needs assessment, matrices, intervention design, and program creation—behavioral determinants were identified through literature review, national data, and community input. The resulting 12-week program integrates twice-weekly family CrossFit sessions, monthly cardiovascular health workshops, and weekly home-based challenges delivered through local affiliates using a train-the-trainer model. Results: IM produced a theoretically grounded and evidence-based intervention targeting individual (self-efficacy, outcome expectations), interpersonal (modeling, relatedness), and environmental (access, social support) determinants. The process resulted in detailed logic models, behavior change matrices, and implementation materials, including family handbooks and coach guides. Conclusions:Lion Hearts represents a scalable, multigenerational approach to CVD prevention that leverages existing community fitness infrastructure. By embedding prevention within family systems and CrossFit affiliates, the program offers a sustainable, replicable model to enhance physical activity, strengthen family health behaviors, and reduce intergenerational CVD risk.